On Thu, Apr 18, 2024 at 8:03 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 18.04.24 12:57, Lance Yang wrote: > > This patch optimizes lazyfreeing with PTE-mapped mTHP[1] > > (Inspired by David Hildenbrand[2]). We aim to avoid unnecessary folio > > splitting if the large folio is fully mapped within the target range. > > > > If a large folio is locked or shared, or if we fail to split it, we just > > leave it in place and advance to the next PTE in the range. But note that > > the behavior is changed; previously, any failure of this sort would cause > > the entire operation to give up. As large folios become more common, > > sticking to the old way could result in wasted opportunities. > > > > On an Intel I5 CPU, lazyfreeing a 1GiB VMA backed by PTE-mapped folios of > > the same size results in the following runtimes for madvise(MADV_FREE) in > > seconds (shorter is better): > > > > Folio Size | Old | New | Change > > ------------------------------------------ > > 4KiB | 0.590251 | 0.590259 | 0% > > 16KiB | 2.990447 | 0.185655 | -94% > > 32KiB | 2.547831 | 0.104870 | -95% > > 64KiB | 2.457796 | 0.052812 | -97% > > 128KiB | 2.281034 | 0.032777 | -99% > > 256KiB | 2.230387 | 0.017496 | -99% > > 512KiB | 2.189106 | 0.010781 | -99% > > 1024KiB | 2.183949 | 0.007753 | -99% > > 2048KiB | 0.002799 | 0.002804 | 0% > > > > [1] https://lkml.kernel.org/r/20231207161211.2374093-5-ryan.roberts@xxxxxxx > > [2] https://lore.kernel.org/linux-mm/20240214204435.167852-1-david@xxxxxxxxxx > > > > Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx> > > Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx> > > --- > > mm/madvise.c | 85 +++++++++++++++++++++++++++------------------------- > > 1 file changed, 44 insertions(+), 41 deletions(-) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index 4597a3568e7e..375ab3234603 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -643,6 +643,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > > unsigned long end, struct mm_walk *walk) > > > > { > > + const cydp_t cydp_flags = CYDP_CLEAR_YOUNG | CYDP_CLEAR_DIRTY; > > struct mmu_gather *tlb = walk->private; > > struct mm_struct *mm = tlb->mm; > > struct vm_area_struct *vma = walk->vma; > > @@ -697,44 +698,57 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > > continue; > > > > /* > > - * If pmd isn't transhuge but the folio is large and > > - * is owned by only this process, split it and > > - * deactivate all pages. > > + * If we encounter a large folio, only split it if it is not > > + * fully mapped within the range we are operating on. Otherwise > > + * leave it as is so that it can be marked as lazyfree. If we > > + * fail to split a folio, leave it in place and advance to the > > + * next pte in the range. > > */ > > if (folio_test_large(folio)) { > > - int err; > > + bool any_young, any_dirty; > > > > - if (folio_likely_mapped_shared(folio)) > > - break; > > - if (!folio_trylock(folio)) > > - break; > > - folio_get(folio); > > - arch_leave_lazy_mmu_mode(); > > - pte_unmap_unlock(start_pte, ptl); > > - start_pte = NULL; > > - err = split_folio(folio); > > - folio_unlock(folio); > > - folio_put(folio); > > - if (err) > > - break; > > - start_pte = pte = > > - pte_offset_map_lock(mm, pmd, addr, &ptl); > > - if (!start_pte) > > - break; > > - arch_enter_lazy_mmu_mode(); > > - pte--; > > - addr -= PAGE_SIZE; > > - continue; > > + nr = madvise_folio_pte_batch(addr, end, folio, pte, > > + ptent, &any_young, NULL); > > + > > + if (nr < folio_nr_pages(folio)) { > > + int err; > > + > > + if (folio_likely_mapped_shared(folio)) > > + continue; > > + if (!folio_trylock(folio)) > > + continue; > > + folio_get(folio); > > + arch_leave_lazy_mmu_mode(); > > + pte_unmap_unlock(start_pte, ptl); > > + start_pte = NULL; > > + err = split_folio(folio); > > + folio_unlock(folio); > > + folio_put(folio); > > + start_pte = pte = > > + pte_offset_map_lock(mm, pmd, addr, &ptl); > > I'd just put it on a single line. start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl); I suddenly realized that putting it on a single line would exceed the 80-char limit. Or: start_pte = pte = pte_offset_map_lock( mm, pmd, addr, &ptl); Thanks, Lance > > > + if (!start_pte) > > + break; > > + arch_enter_lazy_mmu_mode(); > > + if (!err) > > + nr = 0; > > + continue; > > + } > > + > > + if (any_young) > > + ptent = pte_mkyoung(ptent); > > + if (any_dirty) > > any_dirty is never set, likely missed to pass it to > madvise_folio_pte_batch(). > > Apart from that LGTM and this patch is much easier to review now! > > > With above: > > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > > -- > Cheers, > > David / dhildenb >
